Filtration respirators or face masks are used in a wide variety of applications when it is desired to protect a human's respiratory system from particles suspended in the air or from unpleasant or noxious gases. They are also frequently worn by medical care providers to prevent the spread of harmful microorganisms either to or from the user.
Respirators can be classified as disposable respirators that are discarded after use, low maintenance respirators in which the filter is replaceable, and reusable respirators in which some or all of the components are replaceable. Disposable face masks are generally of one of two types--a molded cup-shaped form or a flat-folded form. The flat-folded form has advantages in that it can be carried in a wearer's pocket until needed and re-folded flat to keep the inside clean between use.
The flat-folded respirator face masks are typically constructed from one or more fabric webs arranged to form a face mask blank. Pleats and folds are added to affix the fabric webs into a shape desirable for a face mask. Such constructions may have a stiffening element to hold the face mask away from contact with the wearer's face. Stiffening has also been provided by fusing a pleat across the width of the face mask in a laminated structure or by providing a seam across the width of the face mask.
Some flat-folded face masks include pleats which are centrally folded in the horizontal direction to form upper and lower opposed faces. The face mask has at least one horizontal pleat essentially central to the opposed faces to foreshorten the filter medium in the vertical dimension and at least one additional horizontal pleat in each of these opposed faces. The central pleat is shorter in the horizontal dimension relative to the pleats in the opposed faces that are shorter in the horizontal dimension relative to the maximum horizontal dimension of the filter medium. The central pleat together with the pleats in opposed faces forms a self-supporting pocket.
Another embodiment of a flat-folded face mask includes a pocket of flexible filtering sheet material having a generally tapering shape with an open edge at the larger end of the pocket and a closed end at the smaller end of the pocket. The closed end of the pocket formed with fold lines defines a generally quadrilateral surface comprising triangular surfaces folded to extend inwardly of the pocket. The triangular surfaces face each other and are relatively inclined to each other when in use.
A further embodiment of a flat-folded face mask has an upper part and a lower part with a generally central part therebetween. The central part of the body portion is folded backwardly about a vertical crease or fold line that substantially divides it in half. This fold or crease line, when the mask is worn, is more or less aligned with an imaginary vertical line passing through the center of the forehead, the nose and the center of the mouth. The upper part of the body portion extends upwardly at an angle from the upper edge of the central part so that its upper edge contacts the bridge of the nose and the cheekbone area of the face. The lower part of the body portion extends downwardly and in the direction of the throat from the lower edge of the center part so as to provide coverage underneath the chin of the wearer. The mask overlies, but does not directly contact, the lips and mouth of the wearer.
Molded cup-shaped face masks are made from a pocket of filtering sheet material having opposed side walls, a generally tapering shape with an open end at the larger end and a closed end at the smaller end. The edge of the pocket at the closed end is outwardly bowed, e.g. defined by intersecting straight lines and/or curved lines, and the closed end is provided with fold lines defining a surface which is folded inwardly of the closed end of the pocket to define a generally conical inwardly extending recess for rigidifying the pocket against collapse against the face of the wearer on inhalation.
Disposable face masks often rely on a fixed, elastic strap to secure the mask to the user's head. Headbands for molded cup-shaped or flat-folded face masks must be designed to provide sufficient force to hold the face mask securely in place, while generating pressure within the "comfort zone" on user's of various head or face sizes. Insufficient force can result in leakage around the perimeter of the face mask. Variations in the shape and stiffness of face masks, as well as the size and shape of users make it difficult to determine a universal strap force value. For lightweight disposable face masks, a strap force value of 100-150 grams in a range of 20% to 300% elongation appears to be adequate.
In order to provide a headband with sufficient strap force to create an adequate face mask-to-face seal, within the "comfort zone" of a largest class of users, manufacturers have generally chosen long headband segments constructed from materials with a low modulus. For example, headbands are typically 15.2-35.6 mm (6-14 inches). Common headband materials include natural rubber, polyisoprene, polyurethane and natural and synthetic elastic braids or knits. The headbands are generally longer than the distance between the headband attachment locations whether measured along an axis intersecting the headband attachment locations or as measured along a surface of the face mask blank. Headbands having a length greater than the unit length between the attachment locations of the face mask blank are difficult to assembly on high speed manufacturing equipment for a number of reasons. For example, the slack or excess headband material can interfere with the movement of the face mask blanks along the production line. Compliant elastic headband materials are difficult to handle on high-speed manufacturing equipment. The greater the speed of the manufacturing equipment, the greater the degree of difficulty in registering the headband to the correct attachment locations.
Some elastomeric materials used for headbands, such as natural rubber, are extremely sticky. These materials are frequently treated with talc or other powders to facilitate handling and to increase comfort for the user. The talc can accumulate, however, in the manufacturing equipment. Inconsistent or uneven application of the talc can create difficulties in handling the headband material. Finally, the process of using high speed manufacturing equipment can be further complicated by attaching multiple headbands, such as a head strap and a neck strap, to a single face mask blank.